Barometric instruments commonly provide a method of tracking the current barometric pressure as well as previous barometric pressure values, and changes in barometric pressure over time. This information has proven useful in understanding and predicting changes in the weather.
Barometers commonly provide a manually adjustable index that is set to the current barometric reading to be used as a reference for later readings in order to track changes in barometric pressure over time. This index must be manually set to the current barometric value, and the time noted for later reference. At the next observation it is necessary to manually calculate the pressure change between observations, and reset the index, and record the time of observation in order to repeat the process.
Barographs automatically produce a graph of barometric pressure over time, providing a better understanding of barometric trends without the need to manually set an index and record values. Barometric values and trends are indicated by the position and shape of the graph against background scales for pressure and time. Barograph displays were traditionally printed on paper rolls or charts, while modern barograph displays are commonly electronic.
Barometers and barometric compensation mechanisms have long been associated with precision timekeepers, but the barograph display is not well suited for traditional (analog) clock and watch dials.